1. Field of the Invention:
The present invention relates to a system for preventing unbalance vibrations and synchronous disturbance vibrations in a rotation control system for controlling the radial position of a rotary member suspended by an active magnetic bearing.
2. Description of the Prior Art:
With respect to vibrations of a rotary member in a rotor system radially suspended by an active magnetic bearing, a component responding to any unbalance vibration attributable to residual unbalance is maximum disturbance with respect to unstable vibrations of the rotor system. This unbalance vibration causes an increase in magnitude of vibrations in the vicinity of the natural vibration frequency; and vibration of a structure is provoked when the unbalance vibration synchronizes with the resonance point of the structure. Furthermore, when vibration generating forces are imparted to a stator mounted on a fixing member of a magnetic bearing, vibration of the casing increases. This results in unfavorable effects in terms of unnecessary consumption of electric power and wasteful generation of heat.
An active magnetic bearing typically serves to control a rotary member so that the latter rotates about the geometrical center thereof. The magnetic bearing has, however, three centers, i.e., the geometrical center, the magnetic center and the inertial center of the rotary member. It is difficult to make these centers coincide with one another.
In order to diminish the degree of deviation between each of these centers, efforts are made to provide ordinary dynamic balance and field balance. It is, however, almost impossible to completely eliminate the unbalance which remains in the rotary member. Efforts to eliminate a larger amount of unbalance than is ordinary necessary would result in greater costs.
The surface of a rotary machine becomes corroded and contaminated due to the action of fluid flowing in the rotary machine during its operation and this augments the degree of unbalance. Moreover, an extremely large and abrupt unbalance will occur at the time of such eventualities as blade damage.
Thus, some unbalance inevitably remains in the process of manufacturing a rotary machine, and also some unbalance is newly produced during operation of the rotary machine. A technique capable of reducing adverse influences exerted on a rotary machine due to this unbalance is required in view of the need to improve safety and working conditions in respect of such machines. For this purpose, the rotor should be arranged to rotate about the inertial center so that the vibration caused by any unbalance is decreased.